The present invention relates to an apparatus for cooling high power electronic devices.
Semiconductor devices, such as integrated circuits, power field effect transistors, and the like, are typically attached to a dielectric substrate containing one or more electrical interconnection layers. The substrate is generally made of a ceramic, plastic, or other organic material. The substrate includes an electrical interconnection network that permits the semiconductor device to be electrically coupled to other devices residing either on or off the substrate. The substrate also provides structural support for the semiconductor device. Generally speaking, a substrate containing one or more semiconductor devices is referred to as a xe2x80x9cpackagexe2x80x9d.
FIG. 1 illustrates a conventional package wherein a semiconductor device 10 is attached to the surface of a substrate 12. A solder or thermal adhesive 14 is generally used to attach or couple device 10 to substrate 12. In order to facilitate the removal of heat away from device 10, some packages include a heat slug 16 that is thermally coupled to the back-side of substrate 12 by a thermal adhesive 18.
In high power applications, the attachment of a heat slug to the back-side surface of the package substrate is not sufficient to maintain the semiconductor device within allowable operating temperatures. To increase the rate of heat transfer from high power devices, liquid cooled heat sinks have been attached to the back-side surface of the package substrate. (See FIG. 2). As shown in FIG. 2, a conventional liquid cooled heat sink 30 generally includes a housing 32 containing a flow channel 36 of a uniform cross-section that directs a cooling fluid through the heat sink. Heat is conducted away from device 10 through a solder layer 14, substrate 12, adhesive film 18 and heat sink housing 32. The heat is ultimately removed by convection heat transfer into the cooling medium passing through channel 36.
As integrated circuit technology has improved, substantially greater functionality has been incorporated into the devices. And as integrated circuits have expanded in functionality, the size of the devices have also diminished resulting in higher clocking frequencies and increased power consumption. As a consequence, the integrated circuit devices of today generate more heat while possessing smaller surface areas to dissipate the heat. Therefore, it is important to have a high rate of heat transfer from the integrated circuit package to maintain the junction temperatures of the integrated circuit within safe operating limits. Excessive junction temperatures may affect the performance of the circuit and cause permanent degradation of the chip. Other types of semiconductor devices, such as power field effect transistors, consume extremely high amounts of power (typically in the range of 1 to 3 kilowatts). These devices also require a high rate of heat transfer away from the devices in order to maintain their junction temperatures within safe operating limits. Although conventional liquid cooled heat sinks have proved sufficient in the past, the inherently high thermal resistance path between the heat dissipating device and the cooling medium makes them unsuitable for many of the high power consuming components of today.
Therefore, what is needed is an apparatus that is capable of cooling high power semiconductor devices.
An apparatus for removing heat from an electronic component, such as a semiconductor device, is disclosed.
In one embodiment, a semiconductor device is mounted to a top-side surface of a substrate. A fluid flow channel that is defined at least partially by a portion of the back-side surface of the substrate is provided for passing a cooling medium. This configuration permits the cooling medium to be in direct contact with the back-side surface of the substrate, thus, reducing the overall thermal resistance between the semiconductor device and cooling medium.
In another embodiment, the fluid flow channel is divided into at least two regions. The first region is located near the channel inlet, whereas the second region is positioned adjacent the back-side surface of the substrate at a location opposite the heat generating semiconductor device. The cross-sectional flow area of the second region is less than the overall cross-sectional flow area of the first region. The reduced channel flow area within the second region causes the fluid flow velocity to be increased, thus, enhancing the convection heat transfer within the second region.
In accordance with the present invention, one or more reduced flow area regions may be strategically positioned within a cooling channel that is located below a substrate containing one or more heat generating components. The reduced flow area regions of the channel are positioned adjacent the back-side surface of the mounting substrate at locations just opposite the high heat generating components located along the top-side of the substrate. Among other benefits, this feature permits the thermal performance of the heat removal system to be optimized.